bsdperimeter/pfsense-packages — pull request #261 by phil-davis (2012-06-23 13:47:40+00:00)
Title: error_default_language should just be the language code

In the recent change to using error_default_language, it should have been set to just the language code ('en' 'fr' etc), not to the full dir path.
I have tried this now, blacklisting a site, changing my Firefox preferred language to French and the Squid error page comes back to me in French.